Analysis of the kinetics and voltage-dependency of transient and delayed K+ currents in muscle fibers isolated from the flatworm Schistosoma mansoni

Abstract

There are two distinct voltage-dependent K+ currents in muscle fibers freshly isolated from the human flatworm parasite S. mansoni. Present is a delayed rectifier current with a tau(act) of 17 msec and tau(inact) > 3 sec. The delayed rectifier is very resistant to, steady-state inactivation, with over 40% of the current non-inactivating, and over 15 sec required for the maximum inactivation of the other portion. The current is resistant to block by extracellular tetraethylammonium, is half-blocked by 10 mM 4-aminopyridine, and is insensitive to dendrotoxin. Also present is an ''A'' current with tau(act) <1 msec and tau(inact) < 15 msec. The ''A'' current, like the delayed rectifier current, is resistant to block by external tetraethylammonium and is insensitive to dendrotoxin. Three micromoles of 4-aminopyridine produce a half-blockade of the ''A'' current. These two K+ currents are very similar to a delayed rectifier and ''A'' currents that have been described in a number of lower and more advanced animals.